Poor prognosis cancers including cancers of the lung and glioblastoma show robust overexpresion of Tax Interacting Protein-1 (TIP1). The proposed research is a novel approach to cancer drug development in which we target this chaperone protein that binds to signal transduction proteins that enhance cell viability following cytotoxic therapy. Stress responses in cancer cells are exaggerated over that of normal tissues. Examples are signal transduction pathways that include GRP78, PKC, PLC, Rho and others. Mechanisms by which these proteins dock on the plasma membrane in response to ionizing radiation include motor and scaffold proteins. One scaffold protein that caps the carboxyl terminus of plasma membrane-associated signaling proteins, TIP1 is overexpressed in cancer and translocates to the surface of the cell membrane of cancer cells following exposure to ionizing radiation. The functional domain of TIP1 is the PDZ binding domain which binds enzymes that regulate cell viability such as PLC, PKC, GPCR and Rho. Our preliminary data show that gene silencing of TIP1 and blocking antibodies that bind to the PDZ domain of TIP1 enhance radiation-induced cytotoxicity in cancer but not normal tissues. Anti-PDZ-domain antibodies injected into mice bearing irradiated lung cancer bind specifically to cancer and substantially enhance tumor growth delay over that of controls. We will study antibodies that enhance cytotoxity and improve tumor control. One mechanism by which the anti-PDZ domain antibodies enhance the efficacy of radiotherapy is through interruption of cell viability signal transduction pathways and subsequent programmed cell death specifically in cancer. We will compare antibody fragment (scFv) to whole IgG antibodies that bind to the PDZ domain of TIP1 and determine which antibodies achieve cancer specific binding and enhancement of the efficacy of radiotherapy in cancer without normal tissue toxicity. We will determine the lead human anti-TIP1 antibody fragment that achieves cancer specific binding and cytotoxicity in cancer cells. Our preliminary data show that assays which measure the interaction between anti-TIP1 antibodies and radiation include the clonogenic, and apoptosis assays. We will compare our lead antibodies that are specific to the PDZ domain on TIP1 to determine which is the most cancer specific and cytotoxic. We will determine the efficacy of anti-TIP1/PDZ IgG compared to anti-TIP1/PDZ scFv antibodies in mouse models of cancer. We will determine the role of immune effector cells in the cancer response to anti-TIP1 antibodies. We Hypothesize that IgG could further enhance the efficacy of radiotherapy by activating immune effector cells. We will study mouse models that lack Fc receptors and do not activate antibody mediated cancer cytotoxicity. These mouse models will allow us to determine whether the efficacy of the anti-TIP1 antibodies is a direct effect on cancer cells or whether immune effector cell activation contributes to the therapeutic effect.